6oo MOSSES AND FERNS chap. 



suggestive of the Ferns rather than of the Lycopods. Of 

 course the fact that our knowledge of the Equisetinese is largely 

 based upon the single genus Equisetum, makes it unsafe to lay 

 too much stress upon conclusions drawn from a study of this 

 single type. However, such of the fossil forms as show unmis- 

 takable evidence of belonging to the Equisetinese, conform 

 closely in their structure, so far as it is known, to the living 

 types. The relatively large dichotomously branched leaves of 

 'ArchcEocalamites, the oldest known member of the class, indi- 

 cate that the extremely reduced leaves of the later forms are 

 secondary. The form of the leaves in these ancient Equise- 

 tinese is suggestive of filicinean rather than lycopodinean 

 affinity. 



In the Filicinese the development of the leaves is usually 

 much greater than in either of the other classes, and the origin 

 of the sporophyll is probably different. Bower considers the 

 sporophyll of Ophioglossum, for example, as the homologue of 

 a single sporophyll of Lycopodium, and the whole sporangial 

 spike as equivalent to a single sporangium. With this view the 

 author feels that he cannot agree, and it seems to him more 

 likely that the origin of the Fern-type of sporoph3d;e was quite 

 different from that of the Lycopodinese, and that there is. noth- 

 ing among the Ferns comparable to the strobilus of the latter. 



If we could imagine the meristem at the base of the sporo- 

 gonium of Anthoceros to produce a lateral flattened appendage 

 or leaf, and the foot to develop into a root penetrating the 

 thallus into the earth, we should have a structure not very 

 Unlike a small Ophioglossum. In this case the sporangial spike 

 •would represent, not a single sporangium of Phylloglossum, 

 but the whole strobilus, and the sterile segment of the leaf would 

 then be comparable rather to the sterile leaves (protophylls) 

 than to a single sporophyll. That the spbrophyte in the Bryo- 

 phytes can develop a special assimilatory organ comparable to 

 a leaf, is seen in the apophysis of many Bryales. This is espe- 

 cially conspicuous in some species of Splachnum, where it might 

 almost be compared to a perfoliate leaf. 



The recent discovery of the remarkable Ophioglossum sim- 

 plex (Bower (20)) is especially important in this connection. 

 In this species there is no sterile segment to the leaf, and the 

 sporogenous spike must be considered a terminal structure. A 

 comparison of the younger stages of O. pendulum withO. jjot- 



